Remove old (dead) app list code.

ui/app_list/search_box_model_observer.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_APP_LIST_SEARCH_BOX_MODEL_OBSERVER_H_
 #define UI_APP_LIST_SEARCH_BOX_MODEL_OBSERVER_H_
 
 #include "ui/app_list/app_list_export.h"
 
 namespace app_list {
 
 class APP_LIST_EXPORT SearchBoxModelObserver {
  public:
-  // Invoked when icon is changed.
-  virtual void IconChanged() = 0;
-
   // Invoked when the some properties of the speech recognition button is
   // changed.
   virtual void SpeechRecognitionButtonPropChanged() = 0;
 
   // Invoked when hint text is changed.
   virtual void HintTextChanged() = 0;
 
   // Invoked when selection model is changed.
   virtual void SelectionModelChanged() = 0;
 
   // Invoked when text is changed.
   virtual void TextChanged() = 0;
 
  protected:
   virtual ~SearchBoxModelObserver() {}
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_SEARCH_BOX_MODEL_OBSERVER_H_